The studies contained in this proposal are aimed at the physiological and genetic characterization of a complex transport system which is responsible for the transport of eye pigment precursors into cells where they can be further metabolized. In addition we will assess the timing of the appearance of this transport system during the development of eye imaginal discs. Measurement will be made of the transport of various eye pigment precursors into Malpighian tubules and eye tissue in an organ culture system using standard approaches for studying metabolite transport. The relation between ommochrome precursor transport and pteridine precursor transport will be defined and the number of functional components in this transport system established. Existing eye color mutants will be assayed for their ability to transport the compounds under study. Genetic experiments will be conducted to determine the role of and interaction between specific gene products in this transport system. The developmental timing of the appearance of the transport system will be detemined during the differentiation of cultured imaginal discs. We hope these studies will have relevance to furthering our understanding of membrane changes which may be related to determination and differentiation of imaginal discs, the number of gene products involved in the construction of the transport system and the manner of interaction between these gene products.